<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title></title>
    <style>
        /*一个冒号叫伪类*/
        /*两个冒号叫伪元素*/
        .hi::before{
  content: '先生';
        }
        .hi::after{
            content: '游泳健身了解一下';
        }
        

    </style>
</head>
<body>
    <span class="hi">您好</span>
</body>
</html>